president's address — SECTION H. 159 



substances ought to be removed by a proper system of* 

 scavenging. The partially separate system is in greater 

 favour in England, and it is certainly not generally attended 

 with the disadvantages of the combined system. The rain- 

 water from the back roofs and yards does not carry any large 

 (juantity of silt, and where the gradients are such as to render 

 the sewers self-cleansing with the dry Aveather How, no 

 difficulty from this source need be anticipated. The main 

 objection to the partially separate system consists in the 

 large increase in tlie volume of fluid to be ]irovided for, so 

 that during dry weather, when only the sewage is being 

 discharged, there is a considerable vokime not occupied by 

 sewage in which sewer gas accumulates. The flatter the 

 gradient the greater this volume will become, and where, as 

 too frequently happens, the velocity of the dry weather flow 

 is insufficient to prevent deposit, the sewers become insanitary, 

 and the health of the community using them necessarily 

 suffers. If in any ])roj)osed scheme for drainage the sewers 

 are laid at such gradients that they cannot be self-cleansing 

 with the dry weather How, then it is clear that the scheme is 

 unsatisfactory, and should be modified so as to ensure this 

 self-cleansing velocity. These remarks apply also to the 

 separate system, excepting that the smaller size of the 

 sewers leave a less volume for the accumulation of sewer 

 gas and automatic Hushing by means of specially constructed 

 tanks may and have been successfully applied to prevent 

 and remove deposit resulting from insufficient velocity. 



The Liernur System has been applied to one or two 

 towns in Europe, but it apjiears to me to be exjiensive and 

 unnecessarily complicated. The separation of the solid 

 excreta from the liquid household wastes is, in my opinion, 

 a great mistake, since both consist of organic matter, which 

 in decomposing become offensive and dangerous. The so- 

 called earth-closet system, which is so largely employed in 

 Australia, leaves the liquid household wastes with their 

 burden of organic matter to be dealt with, which is usually 

 done by discharging them into the surface gutters, creating 

 the nuisance with which we are all familiar. 



Shone's Hydro-Pneumatic System possesses the advantage 

 of dealing most efficiently with the sewerage of Hat and 

 low-lying districts, where it is impossible for the Sanitary 

 Engineer to design gravitation sewers, pure and simple, 

 which shall carry away the sewage discharged into them 

 freely and innocuously to one outfall, whether that outfall be 



